Shrink wrap films have seen a wide variety of applications such as CD overwraps, bottle wraps, beverage container wrappings, labels for packaging, especially food packaging, and sealing bands used in tamper evident applications. In an increasingly competitive marketplace, shrink wrap films are being called upon to provide more functionality including packaging design and security, primarily due to the difficulty in forging holograms. Heretofore, shrink wrap films have not been available with holographic patterns which are able to provide strong eye appeal and security simultaneously.
For example, materials are typically rendered holographic via microembossing at elevated temperatures and pressures. As set forth in U.S. Pat. Nos. 4,913,858; 5,164,227; 5,503,792; 5,155,604; and 5,662,986; substrates are rendered holographic under high heat and pressure. Because shrink wrap films are engineered to shrink under heat, it is not possible to emboss such films using traditional techniques.
Further, it is known that films can be imparted with a microembossed structure during an extrusion process. For example, U.S. Pat. No. 5,003,915 teaches the method of creating a holographic image on sheet material via a casting process while U.S. Pat. Nos. 4,913,858; 5,164,227; and 5,155,604 teach an extrusion onto a paper substrate prior to hot embossing. Extrusion of shrink wrap film onto an embossing chill roller is further discussed in U.S. Pat. No. 5,182,069. The disadvantages of such routes include the need for capital equipment such as extruders and, in the latter case, the depth of embossing (up to two orders of magnitude deeper) which can be better described as macroembossing.
Rendering materials holographic via a transfer process is taught in U.S. Pat. Nos. 5,383,687 and 5,662,996. Both inventions therein utilize heat and pressure to achieve their ends and focus on aluminum metallized transfers. U.S. Pat. No. 5,383,687 describes hot stamping holographic foil onto sheets while U.S. Pat. No. 5,662,986 transfers a holographic image to a paper substrate under elevated temperatures and pressures. In both inventions, the heat required is well beyond the temperatures at which the shrink wrap film will begin to contract, rendering such approaches in the context of shrink wrap films inappropriate.
Heretofore, the art provides no means for producing holographic heat shrink elements wherein heat shrink film can be rendered holographic with the use of common coating/laminating equipment.